Loss of oxygen at the Si-SiO2 interface during dry oxidation of silicon

Many studies have shown that silicon oxidizes by interstitial transport of oxygen, that there is an oxygen exchange between the gas (O-2) and the SiO2 -O-2 interface, and that an oxygen exchange between the oxygen molecules in O-2 is catalyzed by the SiO2 surface. A question remains on whether there is exchange between O-2 and the Si-SiO2 interface. We have investigated thi s by oxidizing silicon in three steps: in 210 mbar O-2 at 1100 degrees C; ( 1) in O-16(2) + (2) in O-18(2) + (3) in O-16(2) and measuring the amount of O-18 at the Si-SiO2 interface with nuclear reaction analysis after the sec und and third steps. There was a 20% loss of the O-18 at the Si-SiO2 interf ace in the third step. The lost O-18 was transported interstitially through the oxide to the gas phase, without reacting with the lattice. This cannot be explained by the predominant Deal-Grove oxidation model. We propose a m odification to the Deal-Grove model which allows us to account for the phen omena. The modification can also be used to explain why the oxidation of Si is very sensitive to changes of the surface reactions (contaminants). (C) 1999 The Electrochemical Society. S0013-4651(98)10-057-5. All rights reserv ed.